Conventional transportation fuels and many fine chemicals (e.g. monomers, polymers, plasticizers, adhesives, thickeners, aromatic and aliphatic solvents, etc.) are typically derived from non-renewable raw materials such as petroleum. However, there is increasing concern that the use of petroleum as a basic raw material contributes to environmental degradation (e.g., global warming, air and water pollution, etc.) and fosters overdependence on unreliable petroleum supplies from politically unstable parts of the world.
Thus, biofuels and biomass-derived organic chemical materials provide significant environmental benefits. At present, biofuels tend to be produced using local agricultural resources in many relatively small facilities, and are viewed as providing a stable and secure supply of fuels independent of the geopolitical problems associated with petroleum. At the same time, biofuels can enhance the agricultural sector of national economies. In addition, environmental concerns relating to the possibility of carbon dioxide related climate change is an important social and ethical driving force which is triggering new government regulations and policies such as caps on carbon dioxide emissions from automobiles, taxes on carbon dioxide emissions, and tax incentives for the use of biofuels.
N-butanol is a promising biofuel alternative to gasoline. Several microorganisms produce n-butanol by fermentation. Fermentation is currently used to make acetone, ethanol, isopropanol, n-propanol, n-butanol (also known as “biobutanol”), amyl alcohol, acetic acid, and other organic acids and flavor compounds, for example. While it is well known to use processes such as distillation and gas stripping to effect such separation of the biofuel from the fermentation broth, these conventional processes, particularly distillation, are generally characterized by high capital and energy costs thus often making such conventional processes problematic, for example, it has been noted that in excess of 60% of the heating value of a biofuel, such as butanol, can be “wasted” if conventional separation processes are employed. Additionally, since biobutanol has a higher normal boiling point than water, conventional distillation is not a suitable option for the recovery of the biobutanol.
Therefore, an alternate process for effecting such separations known as pervaporation has received considerable attention as a solution to the aforementioned “waste”. In a pervaporation process, a charge liquid, often a fermentation broth, is brought into contact with a membrane having the property to allow a component of the charge liquid (solution) to preferentially permeate the membrane. This permeate is then removed as a vapor from the downstream side of the membrane film. Transport through the membrane is achieved by the difference in partial pressure between the liquid feed solution and permeate vapor. Solvent/solute separation is achieved due to the difference in relative volatilities and membrane permeabilities of the feed solution compounds. The efficiency of a membrane pervaporation process is measured by its Flux and Separation Factor. Flux is a measure of the weight of solute which passes through the membrane per the membrane area per a unit of time. Separation Factor is the concentration ratio of solute to solvent in the permeate divided by the concentration ratio of solute to solvent in the feed solution.
While polymers such as polyimides, polydimethylsiloxanes and the like have been used to form pervaporation membranes with some successes, to date, none have demonstrated the necessary characteristics to become a commercial success. Hence, there is a continual need for membranes with improved flux and/or separation factors and/or reduced cost in the separation of biofuel.